The invention relates to a method for the analysis of a gaseous component or of a component that can be transformed to gaseous form of a sample. The method provides that the sample is filled into the sample receptacle through the receptacle opening and that an analysis receptacle, which was previously supplied with a tracer reagent, is connected by its receptacle opening via an adapter with the receptacle opening of the sample receptacle, and after which step the component from the sample is expelled into the analysis receptacle. The invention relates, furthermore, to a test kit, in particular a test kit for the implementation of the method described above consisting of the sample receptacle for receiving the sample through a receptacle opening and of an analysis receptacle for receiving the component that is to be analyzed through a receptacle opening, with the analysis receptacle containing a tracer reagent or being able to be supplied with a tracer reagent and being usable as measuring receiving flask in an optical measuring instrument, as well as of an adapter that is used to connect the openings of the receptacles with each other.
It is known in the field of water analytics that certain components in a water sample can be selectively separated from the sample by transforming the components into their gaseous form and to analyze them after this, either directly or indirectlyxe2x80x94in the latter case with optical analysis instruments such as, for example, a photometer. This is done in particular for the determination of carbon; and in this context, the total organic carbon (TOC) is of particular interest. The TOC determination is carried out principally in accordance with DIN EN 1484.
As a rule, the component of the sample is treated in such a manner that the TOCxe2x80x94after prior removal of the inorganic carbon (TIC)xe2x80x94is transformed in the presence of an oxidant, e.g. sodium peroxodisulfate, into its gaseous form, i.e. CO2, and is then expelled from the sample receptacle by way of an inert carrier gas, for example by way of steam distillation or by way of excess reaction gas, into an analysis receptacle. In the analysis receptacle the CO2 is absorbed into a tracer reagent that is present in its liquid or solid form. As a result, the tracer reagent undergoes an optical change which can be analyzed using an optical analysis instrument, e.g. a photometer.
To implement this type of analytical procedure simply and quickly on location with only minimally trained personnel and inexpensive means test kits were developed, as described for example in EP 0 663 239 B1. This test kit contains two receptacles that are realized as glass cuvettes, in particular a sample receptacle and an analysis receptacle, and the receptacles have openings on their top sides respectively which can be locked with screw caps that can be screwed onto the container. The kit also includes an adapter that is to be used in order to be able to achieve a gas-proof connection of the receptacle openings with each other after the removal of the screw caps. The adapter is equipped with a semi-permeable membrane which is permeable for gases, in particular it is permeable for the component that is to be analyzed and for the carrier gas. Also, the membrane can consist e.g. of a hydrophobic material. The tracer reagent can be contained in the analysis receptacle in a previously ready-made and storable form. The sample receptacle can also be supplied with a previously ready-made decomposition reagent that will effect the transformation of the component to be analyzed into its gaseous form.
With the test kit known in the art the absorption of the component that is expelled from the sample occurs inside a closed system, consisting of the two glass cuvettes and of the adapter, which provides a gas-proof connection between the two receptacle openings. Any falsification due to penetrating air from the outside is thereby prevented, which would, due to the CO2 content in the air, lead to incorrect results, in particular with regard to the TOC determination. However, it is disadvantageous that a counter-pressure develops inside the analysis receptacle that counteracts the gas exchange from the sample receptacle to the analysis receptacle and also inhibits the color change on the tracer reagent.
Therefore, it is the subject matter of the present invention to realize a method that works faster and quantitatively with more effectiveness and that results in a more intensive optical change of the tracer regent. Another subject matter of the invention is to provide a suitable test kit for implementing this method.
The first objective is achieved according to the invention in that the analysis receptacle is connected with the outside atmosphere in such a way that a pressure compensation takes place. Thus, the principal concept of the invention provides that the method is no longerxe2x80x94as has been known in the artxe2x80x94implemented inside a closed system, but that the analysis receptacle is selectively opened vis-a-vis the atmosphere while the component is being expelled and, consequently, a partial or complete pressure compensation in relation to the outside atmosphere is achieved. This accelerates the transfer of the gaseous component and of the carrier gas into the analysis receptacle and also results in better absorption of the component on the tracer reagent. In addition, this method ensures that the component reaches the analysis receptacle completely. Also, the connection with the outside atmosphere represents ultimately a kind of safety valve preventing any bursting of the container due to excess pressure.
The realization of the invention envisions that the connection with the outside atmosphere is not established until after the adapter has been attached to the analysis receptacle. This can be accomplished, for example, by removing a covering that blocks the connection.
To accomplish the pressure compensation the analysis receptacle can be perforated, for example, with a ventilation tube.
The invention further envisions that after receiving the sample the sample receptacle is heated, in particular in such a way that a component which is not to be analyzed is expelled, for example inorganic carbon. To support this process, before heating the sample receptacle should be supplied with an expulsion reagent that facilitates the expulsion. The sample receptacle can be heated in unit heaters that are known in the art.
The second part of the objective, which relates to the test kit itself, is achieved according to the invention in that the analysis receptacle is equipped with a pressure relief device, preferably arranged on the end of the analysis receptacle that is opposite to the receptacle opening. The pressure relief device should only be permeable for gases, in particular if a liquid is used as tracer reagent. Excess carrier gas escapes through the pressure relief device, thereby preventing air from entering the analysis receptacle.
The pressure relief device can be realized in a multitude of ways. A particularly simple realization envisions that it is realized as a opening in the receptacle that is closed off with a semi-permeable covering, and the covering preferably consists of a hydrophobic material. It is most useful if the covering is realized as a membrane consisting of e.g. PTFE, PVDF or FEP.
In the alternative, the pressure relief device can be realized as a closed-off opening in the receptacle equipped with a covering that can be perforated, for example in the form of a rubber membrane, in particular consisting of isobutylene-isoprene colpolymer with one-sides or two-sided PTFE or FEP coating. A ventilation tube with a very small dimensioned inside diameter that is part of the pressure relief device should be used for perforating. Since the membrane is self-closing it prevents any outflow of the tracer reagent after the ventilation tube is extracted.
In a further realization of the invention it is envisioned that the covering of the opening in the receptacle features on its outside a protective element that can be removed or pulled off, for example in the form of a paste-on protective foil. This way any gas exchange during storage and transport of the test kit is avoided.
The adapter per se is envisioned in a way that is known in the art, providing it is equipped with a separating membrane that is permeable only for gases in order to avoid any exchange of liquids between the two receptacles. The separating membrane can, for example, consist of a hydrophobic material to accomplish this.
Using the drawings, the invention is illustrated in more detail. Shown is an embodiment for the test kit as well as a representation of the way the method works. Shown are in:
FIG. 1 a sample receptacle, placed inside a unit heater;
FIG. 2 a sample receptacle while filling in the decomposition reagent;
FIG. 3 an analysis receptacle with screwed on adapter, including an enlarged sectional representation;
FIG. 4 the analysis receptacle in accordance with FIG. 3 in a position that is rotated by 180xc2x0, including two versions of pressure relief device in enlarged sectional representations;
FIG. 5 the combination of sample receptacle and analysis receptacle, connected by the adapter;
FIG. 6 the combination in accordance with FIG. 5, placed inside the unit heater, including an enlarged sectional representation of the adapter;
FIG. 7 the view of the combination seen in FIG. 5, including a representation of the same combination rotated by 180xc2x0;
FIG. 8 the combination seen in FIG. 7, placed inside a photometer.